How does our face make the right grimace at the right time? It is not an automatic reflex: the brain prepares the movement long before it appears on the face.
The curve of the smile that lights up our face, the frowning expression of a displeased face, the eyebrows raised in surprise: they seem like spontaneous conformations of facial muscles, but are instead the product of a complex system of neural codes that involves multiple areas of the brain.
A study published in Science offers a better understanding of what’s “behind” facial expressions. Clarifying that, well before a grimace appears on the face, the brain has already decided to express it, thanks to a sophisticated communication system that is always suited to the social context.
Beyond conventions
Researchers at The Rockefeller University in New York were confronted with the idea, which has been in place for decades, that facial expressions are controlled in the brain by two separate systems: one dedicated to deliberate and long-lasting ones, and another that manages emotional and changing ones. It has long been thought that the lateral cortical areas of the frontal lobes of the brain direct voluntary facial movements, made “on purpose”, and that the medial areas of the cortex govern the expressions that arise without us realizing it in accordance with the emotion of the moment.
However, by directly measuring the activity of single neurons in both areas mentioned, the scientists realized that both dealt with both the gestures that we define as voluntary and the emotional ones, and that all this happened long before any facial movement occurred.
Expressions appropriate to the context
Facial gestures, therefore, are not entrusted to two separate neural circuits, but to a single system of neural codes in which different regions collaborate, working hand in hand, providing information on different time scales. There is a neural activity that the authors of the study define as “dynamic”, which reflects the rapid change in facial expressions, and a “stable” one, which functions more like a signal of intent: one must produce that specific grimace because it is socially appropriate and suitable for that context. Together, these two modalities cause the brain to generate effective expressions, which convey specific and socially significant messages.
Restore interrupted signals
In addition to better explaining how motor control of facial expressions occurs and clarifying that facial movements are the result of coordinated work, the study provides elements to help those who, due to brain lesions or disorders affecting the expressive communication of the face, are temporarily deprived of this fundamental form of communication of intentions and their state of mind.
